This invention relates to advanced non-volatile magnetic RAM (MRAM) devices, and specifically to a magnetic tunneling junction (MTJ) yoke structure for use in a MRAM device.
Magnetic RAM has an advantage over convention RAM because of its non-volatility and fast data access. Of all the proposed MRAM structures, magnetic tunneling junction MRAM appears to be the first type of MRAM device to reach production. Motorola aims to sample 4-Mbit MRAM in 2003, eetimes, February 2001. A MTJ includes two ferromagnetic layers which are separated by an insulating tunnel barrier layer. The magnetoresistance (MR) effect is the result of spin-polarization tunneling of conductive electrons between the two ferromagnetic layers. The tunneling current is a factor of the relative orientation of magnetic moments in the two ferromagnetic layers. However, a significant disadvantage to the application of MRAM is the relatively large power consumption required during programming. The large power requirement is the result of the writing process, in which a programming current in the milli-ampere range is required in order to switch a free magnetic layer in the MRAM. Daughton, J. M., Magnetic tunneling applied to memory, J. Appl. Phys. 81(8) pp 3758-3763, April 1997. Data writing in MRAM devices is the result of the application of a magnetic field to a magnetic material, thereby magnetizing the material to one of two memory states. Reading is done by sensing a resistance charge in the magnetized material when a magnetic field is applied. Magnetic fields are created by a current passing through a line external to the magnetic material, as by passing a current through the magnetic material.
U.S. Pat. No. 5,640,343, to Gallagher et al., granted Jun. 17, 1997, for Magnetic memory array using magnetic tunnel junction devices in the memory cells, provides general background information on MTJ devices, and explains how the devices are written to and read from.
U.S. Pat. No. 6,183,859, to Chen et al., granted Feb. 6, 2001, for Low resistance MTJ, describes methods for fabricating a low resistance magnetic RAM.
U.S. Pat. No. 6,304,477, to Naji et al., granted Oct. 16, 2001, for Content addressable magnetic random access memory, describes an MRAM having differential tag program bit lines and a match line.
An MRAM device includes a substrate; plural conductive lines, including a bit line and a word line; and a MTJ stack including a pair of magnetic yoke structures, wherein each of said yoke structures surrounds a conductive line.
A method of fabricating a magnetic yoke in an MRAM structure includes preparing a substrate; forming a first conductive line on the substrate; fabricating a MTJ stack, including fabricating a first magnetic yoke structure about the first conductive line; forming a second conductive line on the MTJ stack; fabricating a second magnetic yoke about the second conductive line; depositing a layer of oxide on the structure; and metallizing the structure.
It is an object of the invention to provide a low power MRAM.
Another object of the invention is to provide a magnetic yoke structure for use in an MRAM.